In a thermal printer, a color print is formed by depositing dye onto a receiver. The dye is typically deposited one color at a time onto the receiver in an overlaid fashion by first depositing yellow, followed by magenta, and followed by cyan. The quality of a print includes how well the individual colors are aligned on the receiver. In other words, if each of the colors is deposited exactly directly on top of the other, there is high print quality. If, on the other hand, the colors are not perfectly aligned, even by a small increment, the image is not its clearest and print quality is lost. Print quality is a concern with all thermal printers, even drum printers where the receiver is fixed to one drum and rotates three times to receive the yellow, magenta and cyan dye.
The alignment problem is more complicated in a scanning thermal printer where the image data to be printed is generated by an imaging system via multiple scanners. First, the image data has to be moved past the sensors and the receiver must be passed by the print heads, thus, there are two independent movements which create two opportunities for misalignment. It is therefore desirable to have a printer in which the movement of the image record is done in concert with the movement of the receiver web. Direct transfer allows printing without storage of image data which is particularly advantageous with long streams of images because of easier movement of data. Accordingly, it will be appreciated that it would be highly desirable to have a scanning thermal dye printer wherein advancing movement of the source image between successive scanning arrays is synchronized with advancing movement of the dye receiving member.
In a scanning thermal printer, there may be three separate printing stations, one for printing each of the colors, yellow, magenta and cyan. When this is so, there is increased possibility of misregistration of the color plane. If the yellow dye is deposited on the receiver first, then there is a possibility that when the receiver web reaches the magenta or cyan printing station, that the printing will not begin at the same point on the receiver as the yellow printing began. It may be necessary to consider the lie of the path that the receiver web travels and also the alignment of the web with regard to the edges of the web. Misalignment of either one will deteriorate the print quality. Accordingly, it will be appreciated, that it would be highly desirable to have a web guiding mechanism to contact the web and change the lithe of its travel path and also to change the skew of the web.